In routers and other portable power machine tools it is common practice to guide the cutting operation from an existing edge or surface of the workpiece to provide a basic reference. The machine tool generally utilizes a rotational cutting tool at the lower end of a vertical shaft. The cutting tool is positioned with respect to the reference by engaging the reference with some kind of matching element, plane, or surface attached to an adjustable positioning device known as a fence. The fence displaces the cutting tool with respect to the reference through an adjustment mechanism so that the desired cutting operation employing the cutting tool can be properly located and guided.
Adjusting the position of the cutting tool relative to the workpiece is a continuing problem, particularly in custom woodworking where high precision calibrated readjustment is often required; furthermore the fence must be convenient to adjust and, once adjusted, it must provide a very rugged structure for uniformity of the routing operation.
It is common for routers to be provided with adjustment capability and indication with regard to vertical settings of the cutting tool to vary the depth of cut; however similar capability is generally lacking with regard to adjustments in the horizontal plane, i.e. setting and readjusting the fence displacement.